I actually picked those up about a month ago, but haven't used them much, not because they don't work, but because of the workout that I had planned for two months in advance. When I did use them, they are a bit more difficult than regular push-ups, and since it was something different, there was that shock to the system which is oh so good.
Bought some last weekend when shopping at Staples of all places. Been doing 100 pushups every AM, and wanted to try something new. They work pretty good. I think they work different parts of the pecs than regular pushups. Really sore the first couple days, which I take to be a sign I'm doing something right.